The present invention relates to a method of producing accumulator plates having respective connection appendages or lugs, from a virgin strip made, for example, of a metal alloy such as a lead alloy.
More specifically, the subject of the invention is a method in which a virgin strip is fed through an expansion machine having at least one expansion punching tool and an associated complementary tool or matrix, the machine being caused to operate in synchronism with the movement of the strip so as to produce a strip formed as a grid having a non-expanded central portion or band and two lateral, longitudinal grid portions.
A method of this type is known, for example, from British patent GB-B-2 200 069.
According to the prior art, in order to produce the connection appendages or lugs of the individual plates, a plurality of openings or windows, separated by transverse bridges which are to form the connection appendages or lugs, is formed in the non-expanded, central portion of the grid strip, downstream of the expansion machine.
These openings or windows are typically formed by a punching press disposed downstream of the machine for the expansion of the strip.
In conventional plants of the type described above, the operation of the punching press for forming the above-mentioned openings or windows is completely unrelated to that of the expansion machine so that, in the plates thus produced, the connection appendages or lugs are positioned completely randomly relative to the nodes of the meshes of the grid portions of the plates. This leads to the disadvantage that it is not possible to ensure that the plates formed in succession from the grid strip are cut in the region of a transverse row of nodes of the meshes. Cropped limbs or ends are therefore inevitably formed at two opposite ends of each plate and these are dangerous since, in a battery of accumulators, they may cause a contact between plates with different polarities.
Expansion machines for producing grid strips in which the strip is supplied by means of a pulling device disposed downstream of the expansion punching tool and pulling the strip along with continuous motion have been proposed. In these machines, the expansion punching tool is subjected to two combined movements, that is: a vertical oscillatory movement for the cutting of the strip and a horizontal oscillatory movement parallel to the direction of movement of the strip so that the meshes are cut with zero relative velocity between the tool and the strip. In these machines, a rotary cutter is also installed downstream of the expansion tool and punches the windows in the central portion or band of the grid strip.
These machines also suffer from the disadvantage described above connected with the random positioning of the connection lugs relative to the nodes of the meshes of the grid portion in each plate.
In order to remedy the disadvantage outlined above, the use of expansion plants in which a plurality of uniformly spaced openings are provided in the virgin strip beforehand, for example, along its longitudinal centreline, has been considered. In this case, the strip can be fed through the expansion machine by means of an indexed pulling wheel having a plurality of peripheral projections which engage in the holes pre-formed in the strip, bringing about a stepped movement thereof. During the subsequent step of punching of the windows in the central band of the grid strip, a device similar to the indexed wheel is used for feeding the strip so that the windows are always formed in the desired positions relative to the meshes of the grid portion of the plates. This method is in fact quite complex and does not generally permit good productivity.
An object of the present-invention is therefore to propose a method and a machine which prevent the disadvantages of the solutions outlined above.
This and other objects are achieved, according to the invention, by a method the main characteristics of which are defined in appended claim 1, as well as by a machine the principal characteristics of which are defined in claim 4.